The present invention relates to internal-combustion engines whose exhaust line comprises at least one catalyst.
The purpose of a catalyst generally consists in activating the oxidation (COHC) or reduction (NO.sub.2) reactions which take place in the natural state and which lead to the deposition of polluting bodies inside the exhaust line but some kinetics of which are too slow at the temperature of the exhaust gases.
A catalyst or catalytic muffler placed on the exhaust line of an engine is intended to reduce the emissions of some pollutants such as CO, HC, NO.sub.x, . . . which are present in the exhaust gases.
However, when cold, a catalytic muffler has no effect on the pollutants released by the engine. A catalytic muffler must therefore reach a minimum temperature to start taking effect. There is thus a delay period known as priming delay during which the pollutant emissions are not decreased by the catalyst. This delay must therefore be as short as possible. The triggering or priming time of a catalytic muffler is commonly about 2 minutes.
Standards in force in most industrialized countries establish the limits allowed for the emission of pollutants.